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Author Topic:   How DNA replication occurs and stages?
catalogpeptide01
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posted 04-08-2015 10:04 AM     Click Here to See the Profile for catalogpeptide01   Click Here to Email catalogpeptide01     Edit/Delete Message Reply w/Quote
Deoxyribonucleic acid (DNA) synthesis means creation of a new DNA molecule, which happens in the synthesis phase (S PHASE) of cell cycle.
DNA replication as the term suggests is a process in which DNA is copied to create other similar DNA molecules. Replication is an important method because, whenever a cell divides, it is essential that two daughter cells must contain the similar genetic information, or DNA, like parent cell.
To understand the process of DNA replication we need to understand the whole process which is divided into different stages. There are certain problems which may occur during the DNA replication process that can be cleared or corrected by the checkpoints, formed by the defense mechanism of our cells.
S Phase:
S phase or synthesis phase is the initial stage of the DNA replication process. Synthesization is the basic and starting point to the process of replication. The purpose of S phase is to originate an identical double-stranded DNA molecule. The identical DNA strand is conceived by using each side of the double-stranded DNA strand as a template. The first step in the procedure is to break the double-stranded DNA, which is possible with the use of DNA helicase enzymes. Now single stranded DNA molecule is read by DNA polymerase which incorporates the complementary nucleoside-triphosphate in a reverse position. This creates two similar double-stranded DNA molecules, both of which contains one template and newly formed (synthesized) strand.
Replication of DNA:
The double-stranded DNA strand is opened up by helicase and DNA synthesis takes place at the Y-shaped replication junction in the five prime (5’) to three prime (3’) direction. The replication junction refers to the formation that takes place when the original double-stranded DNA strand is being broken into two branching prongs. DNA has a direction and it is because of its asymmetrical molecule and the direction of the strand is decided by the orientation of the deoxyribose sugar. DNA is always synthesized in forward direction, beginning with the 5’ end because it is an exposed phosphate group on the 5th carbon in deoxyribose, and synthesizes down to the 3’end of the strand which is characterized by a free hydroxyl group located in the third position on the carbon. Since DNA strands run against-parallel line, the 3’ to 5’ template strand will be replicated constantly and is called the leading strand.
Problems during synthesis of DNA:
DNA replication is a very delicate system or process and is the only source of broken chromosomes and DNA recombination. The rearrangements of broken chromosomes and DNA recombination are mostly harmless, as they are fixed at checkpoints within the cell cycle, but there are certain defective cells which continue to divide, leading to a tumor. Fortunately, human cells are very effective in their defense mechanism which minimizes the errors during replication process. Any kind of error in the process is picked by checkpoints, which will stimulate a surge of events, shutting down the cell cycle until it is fixed.
For more Information visit on- http://www.biosyn.com/dna-synthesis.aspx

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